1. Field of the Invention
The present invention relates to a method for straightening rolled material, such as, sheets, strip, plates, sections, girders, etc. The method includes measuring the straightening forces of at least one of the straightening rolls in a roll straightening machine and adjusting the positions of the straightening rolls in accordance with the measured values.
2. Description of the Related Art
During the straightening procedure, vertical forces among other forces occur at the straightening rolls, wherein the vertical forces depend upon the properties of the material to be straightened, the dimensions of the straightening machine and the selected adjustments of the straightening rolls. These forces cause an elastic deformation of the straightening machine, particularly of the rolls, the bearings and the housing, resulting in a change (spring-back) of the roll positions which initially are usually adjusted without material to be straightened. Accordingly, the roll adjustments must be selected in such a way that the desired straightening effect is achieved with the changed adjustments occurring under load. Deviations of the properties of the material entering the straightening machine (temperature, width, thickness, modulus of elasticity, strength, yield point, etc.) from the values determining the selection of the roll adjustments usually lead to undesirable straightening results. For example, a change in strength leads to a changed curvature of the material leaving the straightening machine. Since changed properties of the material to be straightened result in changed straightening forces which, in turn, lead to changed spring-back values and, thus, to changed effective adjustments, it is apparent that the stability of the straightening result with scattered product parameters is essentially determined in part by the spring-back behavior of the straightening machine. The above results are based on practical experience in the past. For example, in high-strength, thick sheet metal, the spring-back may be even the dominating component of the effective roll adjustment.
The stiffness of the machine is also used for the approximate description of the spring-back behavior. A stiffness matrix is particularly suitable for the linearized description of the dependencies between individual roll forces and individual roll spring-backs. In addition, the elements of the matrix may depend on the respective point of operation. Computations have shown that a relationship exists between the property changes of the material entering the straightening machine (yield point) and the straightening results (curvature of the discharged material). For example, different machine stiffnesses have substantially different patterns. Similar relationships can also be shown for the parameters which depend on the thickness and width of the material. With respect to method technology, it is always an advantage if the scattering of the parameters have as little effect as possible on the bending process, i.e., functional patterns which are as flat as possible.
In straightening sheets, strips, plates, sections, girders, etc., the process is determined by the vertical positions of the straightening rolls selected in dependence on the desired straightening result and the properties of the material being straightened. Depending on the type and construction of the straightening machine, the upper and lower straightening rolls can be adjusted individually or jointly, as described by German Offenlegungsschrift 33 08 616 which discloses a method and an arrangement for straightening sheet metal. In addition to wedges and spindles, hydraulic piston-cylinder units can be used as adjusting devices.
In the known method described above, the adjustment and correction of the straightening roll gap is effected by means of control wedges which are in connection with pressure cylinders and spindle drives as displacement devices. The control wedges are arranged so as to extend in longitudinal direction of the straightening rolls and, therefore, are in the same manner in operative connection with the two bearings of the straightening roll. This results in one disadvantage that, when increased eccentric loads of the straightening rolls occur during the operation of the rolling mill due to changes of the cross-section and/or the strength of the rolled material, these eccentric increased loads are not immediately measured and, thus, cannot be corrected by adjusting the rolls without a time delay. This leads to an increased production of deficient finished products which must either be subjected to an expensive finishing operation or must again be melted down as waste.
Moreover, in this known method, the adjustment and correction of the straightening roll gap is not effected automatically, but manually. This causes a further time delay of the correction being made at the straightening rolls and increases the production of deficient final products. Also, in this known method, it is not possible to prevent elastic deformations of the straightening machine, particularly of the rolls, the bearings and the housing which not only negatively affects the straightening result of the material to be straightened, but also negatively affects the straightening machine.
It is, therefore, the primary object of the present invention to provide a method of the above-described type in which deviations and scattering of the properties of the material are determined without time delay and the consequences thereof are eliminated.